1. Field of the Invention
One embodiment of the present invention relates to a module substrate and disk apparatus.
2. Description of the Related Art
As a conventionally known substrate, there is a module substrate in which active element parts including bare chips are mounted in a circuit pattern of a printed wiring board. When mounting active element parts in the circuit pattern of the print wiring board in the conventional module substrate, first, the electrodes of the active element parts are soldered to the circuit pattern of the printed wiring board. Then, a resin solution for formation of underfill is injected between the printed wiring board and the active element parts, and cured to form an underfill. In this manner, the mechanical fixation and the like of the active element parts to the printed wiring board are assured.
However, while injecting the resin solution for forming underfill, the resin solution, in some cases, flows out from the region where the active element parts of the printed wiring board are mounted to spread to peripheral parts, and therefore the following problems may occur. That is, for example, in a module substrate that uses a printed wiring board in which a rigid insulating substrate made of an epoxy resin as its main material is built, the spreading of the underfill to peripheral parts creates a trouble in replacement of an active element part. On the other hand, in a module substrate that uses a printed wiring board in which a flexible insulating substrate made of a polyimide film is built, the part of the substrate where the underfill spread loses its flexibility since the underfill is made of a cured resin of a high property as its main ingredient. Further, if the film is bent at a part where the underfill is spread, the portion of the underfill peels off to create dust, and therefore in the case of a disk apparatus, a medium loaded in the apparatus may be adversely affected.
As a solution to the above-described problems, U.S. Pat. No. 6,707,162 discloses such a technique that an alignment region is provided for each circuit pattern portion of a printed wiring board in which active element parts to be mounted are fixated with an underfill, so as to expand the intervals. Another solution is disclosed in U.S. Pat. No. 6,291,264, in which a trench is provided to stop flow-out of an underfill during the fixation of active element parts with the underfill. However, as the density of mounted parts has been increased, such an arrangement of the parts that considers a clearance for the flow-out of the underfill solution, or the formation of a trench is very difficult in practice.
On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 2001-102700 discloses a flexible printed wiring board that can prevent disconnection even after a great number of times (for example, about 10,000 times) of open/close operation as in the case of a mobile phone. This flexible printed wiring board is provided for, for example, a hinge portion of a foldable type mobile phone, which is repeatedly bent and stretched, and has such a structure that a metallic layer of a circuit pattern or the like, is interposed between a pair of films and at least one of these films is made of a friction resistance member or an abrasion resistance member.
Further, Jpn. Pat. Appln. KOKAI Publication No. 6-326445 discloses a circuit board in which a heat-resisting insulating agent having such properties that reject fused solder (that is, for example, a heat-resisting insulating agent that is made of an amorphous fluororesin as its main component) is attached to the surface of each of solder-resist films formed to be distant from each land of a wiring pattern.